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FROM BULLETIN OF THE UNITED STATES BUREAU OF FISHERIES : VOLUME XXXII, 1912 
Document 786 :::::::::: : : : Issued February 18, 1914. 



THE EFFECT OF WATER-GAS TAR ON OYSTERS 



By Philip H. Mitchell 



199 



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THE EFFECT OF WATER-GAS TAR ON OYSTERS. 

By PHILIP H. MITCHELL. 

For a number of reasons it has become desirable to know the effects of oily and 
tar-like wastes on marine life of economic importance. Damages have been claimed 
for pollution of oyster beds by wastes from the manufacture of gas. A report to the 
Rhode Island shellfish commission has attributed to water-gas tar harmful effects to 
oysters in Narragansett Bay." 1 Tar of various sorts is used for coating piles or stakes, 
which might be in proximity to shellfish. Oily wastes are constantly escaping from 
passing craft in inland waters. 

The present investigation does not cover the entire subject, but is confined to one 
important phase — the effect of water-gas tar on oysters. The experiments made 
during the summer of 1912 at the laboratory of the Bureau of Fisheries at Woods Hole 
could not then be carried further. 

The tar was obtained from the separator at the works of the Providence Gas Co. 
on October 25, 1910, and was a mixture of the heavier and lighter tars as obtained 
in the manufacture of water gas, using an average temperature of 1 ,450° F. An analysis 
of tar taken under comparable conditions from the same separator at another time 
showed, according to the records of the Providence Gas Co., the following analysis: 

Per cent 
Specific gravity at 65.5° F., 1. 050. by volume. 

Water 7.65 

Light oil at 200° F 13. 95 

Dark oil at 400° F 42. 20 

Medium pitch 36. 20 

Free carbon 2.70 

Three series of experiments were made. In the first, oysters were exposed to 
water-gas tar in stagnant sea water; in the second series they were exposed to the 
tar in running sea water; while in the third small amounts of water-gas tar were intro- 
duced inside the shells of oysters. 

SERIES I. 

Experiment 1. — An oyster, marked with a file for identification, as were all the 
oysters used in these experiments, and weighing 83.2 grams, was put into a battery- 
jar with 40 c. c. of water-gas tar and 2,500 c. c. of sea water. On the following day 
the water was changed by the method used in all the experiments of this series. A 
siphon delivered sea water from an aquarium to a point about 2 inches from the bottom 
of the jar, while another siphon at the same time drew off water from the middle of the 
jar. Water was allowed to run thus 10 to 15 minutes. As the tar stuck to the sides 

o Field, G. W. In Annual Report ol the Commissioners of Shell Fisheries. Rhode Island, 1906, appendix D. p. 46-64. 

201 



202 BULLETIN OF THE BUREAU OF FISHERIES. 

and bottom of the jar, or, in the case of the lighter more oily portions, floated on the 
surface of the water, none, or very little of it, was removed while the water flowed through 
the siphons. The water, therefore, was almost completely changed without removing 
the tar. Shortly after the water had been changed the oyster was seen to be slightly 
open, but could close at the slightest jar. The water was changed in this manner once 
or twice daily for 10 days, The oyster was often seen partly open during this time, 
but would always respond to a mechanical stimulus by closing. After 10 days the 
water was no longer changed, but was left entirely stagnant. At the end of two weeks 
under these conditions the oyster seemed to be affected. It now remained continuously 
open, and appeared unable to close when stimulated. A few days later it showed signs 
of putrefactive disintegration. 

Experiment 2.— An oyster weighing 63.7 grams was treated exactly as in experi- 
ment 1. The results were quite the same, except that when the water was left entirely 
stagnant disintegration set in after five days. 

Experiment 3. — An oyster weighing 71.6 grams was treated as in the preceding 
experiments, except that the tar was smeared all over the inside of the jar and on the 
oysters. After 24 hours the oyster was found wide open and unable to close when 
stimulated. It was removed from the jar, and was seen to have its mantle greatly 
retracted. It would spring open when closed by hand. It was washed and put into an 
aquarium in running sea water. Two days later it appeared to be entirely recovered, 
as it would close normally when stimulated. It was then put back into the jar of sea 
water and tar in which it had been at first. It was now kept in this jar during six days, 
with the water changed once or twice daily. At the end of this time it had again lost 
the ability to close normally, but when put in the aquarium once more it again appar- 
ently recovered. About three weeks later, however, it became disintegrated. 

Experiment 4. — An oyster weighing 95 grams was arranged exactly as in experi- 
ment 3. The results were quite the same, that is, after 24 hours it refused to close, 
but recovered when put in the aquarium of running sea water. Some weeks later, 
however, it died. That its death was due to the tar is not certain, because at that time 
other oysters in the same aquarium died without any previous exposure to tar. 

Experiment 5. — An oyster weighing 78.7 grams was treated exactly as in the preced- 
ing experiment. It, too, became unable to close after 24 hours, and when put in run- 
ning sea water entirely recovered. At the end of the summer, nine weeks later, it 
seemed entirely normal and had a normal appearance when opened. 

Experiment 6. — An oyster weighing 62 grams was treated exactly as in the preced- 
ing experiment. The result was slightly different in that the oyster did not begin to 
show a tendency to remain open until after three days, and became entirely unable to 
close after five days in the tarry water with daily changing of the water. It was then 
put in running sea water and began to disintegrate a few days later. 

Experiment 7. — An oyster weighing 70.8 grams was put into a battery jar with 20 
c. c. of the tar not in contact with it and 2,500 c. c. of sea water. The water was changed 
daily during the next 10 days. It was then left stagnant during 8 weeks. The oyster 
was sometimes observed to be open, but would then close if jarred. At the end of that 



EFFECT OF WATER-GAS TAR ON OYSTERS. 



203 



time it was cleaned and dried and found to weigh 71.6 grams. It had formed new shell 
all around the edge. Opened it gave no smell of tar, the heart was beating and the 
mantle was normally sensitive to mechanical stimuli. Part of the heart and portions 
of the gills were discolored. 

Control experiment. — An oyster weighing 72.4 grams was put in a battery jar with 
2,500 c. c. of sea water. The water was changed during the next 10 days as in the pre- 
ceding experiment and was then left stagnant during 8 weeks. Examination then 
showed no noticeable new shell, but the heart, gills, and mantle were quite normal. 

The experiments of this series indicate that when considerable quantities of 
water-gas tar are in intimate contact with oysters in stagnant water serious or fatal 
effects are produced. Under these circumstances the oyster can not use its natural 
defense against a relatively or entirely insoluble substance. When the water is stag- 
nant, there is little opportunity to eject such substances and free the organism from 
them. As will be shown later, the oyster can rid itself of water-gas tar when in running 
sea water. When the tar can not be ejected it seems to produce an effect similar to 
paralysis, so that the initial symptom is a failure of the adductor muscle to respond 
to stimulation of the sensory nerves. No conclusions as to the structures specifically 
affected can be drawn from these experiments. Whether the fatal effects produced in 
five of the above experiments were due to a direct toxic effect of water-gas tar, or to 
some indirect effect also, does not appear from these experiments. 

SERIES 11. 

Method. — Two oysters were put in each of four battery jars. Each jar was arranged 
with two siphons, one bringing sea water from an aquarium to the jar with the lower 
end of the siphon about 2 inches below the level of water maintained by the other siphon, 
which carried water from the jar to a sink. The running water therefore tended to 
carry off the light floating oils but left the heavier tar sticking to the bottom and sides 
of the jar. The siphons were so arranged that each jar contained constantly about 
2,500 c. c. of sea water. Into each jar there were put 30 c. c. of water-gas tar mixed 
with sand and thoroughly smeared over the bottom and sides of the jar and on the 
shells of the two oysters. From time to time during the following weeks small amounts 
of tar were added to replace that carried away by the siphons. After remaining in 
the jars as described during nine weeks the oysters were cleaned, weighed, and examined. 
Comparison of their weights at the beginning and at the end of the experiments is given 
in tabular form : 







Initial 


Final 


Jar. 




weight. 


weight. ] 






Grams. 


Grams. 




: 


98.0 


99.0 : 


1 


47-8 


47-8 




i 


92 





92. 




51 


4 


52.3 






96 


8 


94.0 


3 


61 


8 


6;. ; 


-I 


! 


101 
43 


i 
2 


IOO. 7 
44-3 | 



204 



BULLETIN OF THE BUREAU OF FISHERIES. 



That these variations in weight have no special significance is indicated by com- 
parison with the variations in the weights of oysters kept in the aquariufn during the 
summer but not exposed to tar. 



Initial 
weight. 


Weight after 
five weeks. 


Grams. 

66.5 
76. 
244.0 
147.0 


Grams. 
66.0 
76.5 
243.0 
151-0 



When opened all were found to be normal in appearance and function. No odor 
of tar was detectable in the shell contents of the oysters, although an abundance of tar 
was left in the jars at the end of the experiment. Smears of tar were also still present 
on the outside of the oyster shells. 

These experiments indicate that even intimate contact with water-gas tar does not 
injure oysters in the course of nine weeks, provided facilities for defense in the form of 
moving water frequently renewed are available. 

SERIES in. 

Experiment 1. — A small oyster was first pried open and injected with 0.5 c. c. of water- 
gas tar. It was then put in a jar of running sea water. It remained tightly closed 
during the next two hours. On the next day it was found to be quite normal. It was 
open and apparently feeding, but closed when stimulated. Drops of tar near it indicated 
that the foreign material had been ejected. One week later it still appeared entirely 
normal. It was then again injected with 0.5 c. c. of tar, and was now put in stagnant 
sea water. Four days later it did not, when stimulated, close as readily and tightly as a 
normal oyster. It was then opened and found normal in its heartbeat and in con- 
tractility of the bivalve muscle, but the mantle was not normally responsive to mechanical 
stimulus. 

This experiment indicates that when an oyster ingests tar and can not get rid of it 
because the surrounding water is stagnant, some impairment of the sensory apparatus 
in the mantle results. This interferes with certain activities of the oyster, prevents 
normal closure, and eventually causes degeneration of muscular and other tissues. 

Experiment 2. — Three medium-sized oysters were each injected with about 1.5 c. c. 
of water-gas tar and then put in separate jars of running sea water. Some time after 
they were seen in each case to open slightly and in a few minutes close violently so as to 
eject masses of tar. This process was repeated a number of times in the course of one 
to three hours after injection. They then remained constantly closed for some time, but 
were found normally open on the following day. They were left in the running sea 
water for a period of eight weeks and behaved throughout that time like control oysters 
in the aquarium. As it was then necessary to terminate the experiments, the oysters were 



I 



EFFECT OF WATER-GAS TAR ON OYSTERS. 



205 



opened and carefully examined. They were found to be normal in color, odor, heartbeat, 
responsiveness of the mantle, ciliary movement, and in short in every respect. 

This experiment distinctly indicates that water-gas tar in considerable doses is 
harmless to an oyster in running sea water. The conditions of this experiment more 
closely resemble those of the native habitat of the oyster than do those of the preceding 
experiment, because tides and other currents over oyster beds maintain a constant 
movement and a continuous changing of the surrounding medium. 

Experiment 3. — A medium-sized oyster was injected with 1 c. c. of water-gas tar, 
which was distributed all around the mantle. It was then put into about 1,500 c. c. 
of sea water and carefully observed. During the next five hours it did not visibly open 
and no tar escaped from it. On the following day, however, a few drops of tar were 
floating on the surface of the water. During the next two days the oyster was only 
infrequently observed and was not seen open, but on the third day it was found nor- 
mally opened and able to close when stimulated. It was left in the same sea water 
during the next two weeks. It had then developed the usual symptoms of imperfect 
closure and when opened did not show a normally beating heart or a responsive mantle. 
This experiment confirms the first one of this series. 

EFFECT OF WATER-GAS TAR ON THE DISSOLVED OXYGEN OF SEA WATER. 

It seemed possible that tar and similar substances might in a measure reduce the 
oxygen content of water so as to affect shellfish. Mixtures of tar and sea water were, 
therefore, allowed to stand for varying periods of time and then tested by Winkler's 
titration method to measure the quantity of dissolved oxygen in the water. The 
experiments are summarized in the following table. Three liters of sea water were used 
in each case. 



Amount of 
water-gas 
tar used. 


Time mixture 


Oxygen re- 


was allowed to 


maining in 


stand at room 


water at end 


temperature. 


of the time. 


Cubic 




Parts per 


centimeters. 


Hours. 


million. 


200 


20 


6.61 


200 


24 


6. 10 


200 


45 


. 00 


200 


130 


.08 


SO 


40 


2. 71 


SO 


45 


1. 10 


50 


130 


.08 


None. 


40 


° 7. 10 


None. 


45 


«8. 09 


None. 


130 


"8. 26 



a Control, sea water alone. 



These experiments show that the tar can cause the disappearance of dissolved 
oxygen in sea water. How potent a factor this may be in causing the effects of the 
tar on oysters in stagnant water it is not, however, safe to say. Oysters, as the author 
has shown, are remarkably resistant to lack of oxygen and do not when deprived of it 



U ML I 40U OMO 

\ 
206 BULLETIN OF THE BUREAU OF FISHERIES. 

show inability to close except in the advanced stages of oxygen starvation. /That oxygen 
consumption by tar may help to account for the fact that oysters are injured by stag- 
nant tarry water, while they are uninjured by the tar in running sea water, is quite 
probable. In the natural habitat of the oyster, however, it seems quite impossible 
that the slight reduction of dissolved oxygen which small amounts of tar could effect 
would alter the results of oyster culture. 

CONCLUSION. 

These experiments show no noticeable effects of water-gas tar on oysters in con- 
stantly renewed sea water. This is true in spite of the fact that large amounts of tar 
mixed with stagnant sea water, or small amounts injected into oysters which are kept 
in stagnant water, do cause serious or fatal effects. Considerable quantities (1.5 c. c.) 
may be put inside the shell of an oyster kept under conditions resembling those of its 
natural habitat without causing any effect. The harmlessness of the tar under these 
circumstances is due apparently to the ability of the oyster to rid itself of such foreign 
matter. In stagnant water the organism can not be effectively washed out, and effects 
involving a loss of sensitiveness in the mantle result. That consumption of the dis- 
solved oxygen in the stagnant water by tar may have some effect on oysters is a 
possibility. 



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